API: Add endpoint to reset runner token with old token

What does this MR do and why?

By providing the old token, as long as it is not expired, the user proves that they have the rights to the runner, and can reset the runner token. This allows them to reset the token without a PAT.

Issue: #30942 (closed)
Issue: #345427

This depends on !71607 (closed).

How to set up and validate locally

1. Create a runner

2. Run the following to reset the runner's authentication token:

   $ curl --form 'token=<old token>' http://gitlab.example.com/api/v4/runners/reset_authentication_token

3. See the new token in the JSON response

MR acceptance checklist

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